The present invention relates to rail gun systems and cartridges therefor and, more particularly, to a cartridge having a projectile for being accelerated by an electromagnetic rail gun system.
An electromagnetic rail gun is, in essence, a linear direct current motor. A prior art rail gun includes a pair of spaced copper rails, the breech ends of which are connected with a source of direct current. A projectile carries at its trailing end an armature in the form of a conductive sliding block. As current flows from the breech end of the first rail, through the block, and back toward the breech end of the second rail, the magnetic field provided by current flowing through the rails interacts with the current flowing through the sliding block to produce a force (the Lorentz force) which accelerates the projectile toward the muzzle end of the rails.
One significant advantage that electromagnetic rail guns have over more common guns relying on the detonation of an explosive charge to accelerate a projectile, is greatly increased muzzle velocity. The latter type gun is limited by the speed at which gases resulting from the detonation are able to expand. This, in a practical gun, results in a maximum muzzle velocity of about two kilometers per second. Theoretically, and without taking into account the strength of the materials of the rails and projectile, the limit of the muzzle velocity of a rail gun in vacuum is the speed of propagation of a magnetic field (approximately the speed of light). Muzzle velocities of small bore rail guns have exceeded 10 kilometers per second. Particularly in military applications, increased muzzle velocity is of paramount importance because it affords the weapon greater range and lessens the time a target has to undertake evasive action.
Prior art rail guns are typically more on the order of laboratory curiosities than practical weapons. They are limited to a single shot capability and often require replacement of the rails after each firing due to arc damage when the projectile is accelerated from rest. More specifically, with the rails deenergized, the projectile with its sliding block armature is manually loaded into the breech end of the gun. A crowbar switch is then closed to cause energization of the rails by a primary power source, such as a large capacitor bank. Upon closing of the switch, very high current (up to 1/2 to 3/4 mega amperes) flows through the breech portion and the rails and the projectile armature.
Because the projectile starts from a static condition and is accelerated generally throughout its travel in the rail gun, the projectile has a high dwell time in the breech end of the rail gun, typically resulting in arc damage such as pitting, erosion or melting in that portion of the rails. Additionally, acceleration of the projectile from a rest condition requires the use of a longer barrel for the projectile to achieve a desired velocity. The use of a longer barrel is undesirable because it necessitates a longer current path through the rails, causing greater heating losses and the storage of greater energy in the magnetic field between the rails, thereby reducing the efficiency of the rail gun. Moreover, a longer rail gun takes up more space, uses more material and has greater weight.
Previous rail guns have accelerated ballistically unstable projectiles, typically encased in sabots. The sliding block armature of the projectile has shortcomings in that it can move out of mutual contact with both rails, hence increasing the resistance to current flow, and exhibits a large drag force on the rails when in contact therewith. Furthermore, the continued presence of the relatively heavy armature at the trailing end of the projectile does not permit a proper weight distribution as required for a true ballistic projectile. It is simply too tail heavy for proper stable flight.
One proposed rail gun used the expansion of light gas caused by initiation of an electrical arc through it to accelerate the projectile initially, with the rail gun further accelerating it. This rail gun also was limited to single shot capability and, besides requiring an external source of electrical power, required an external source of the light gas. For a further description of the structure and operation of this rail gun, reference may be made to the U.S. Pat. No. 3,431,816.
In summary, such prior art rail guns, and the projectiles for use therewith, are not particularly attractive to the military as an alternative to the much more common propellant discharge guns. The prior art rail guns typically have only single shot capability and must be, at least partially, disassembled before insertion of a second projectile. Such rail guns also may require external supplies of propellant, such as a light gas, for initially moving the projectile. In addition, previous electromagnetically accelerated projectiles were non-ballistic laboratory devices, many of which were fired in a vacuum.